1. Technical Field
This application relates in one aspect to a method for determining vision defects and for collecting data for correcting vision defects of the eye by interaction of a patient with an examiner and apparatus therefor.
2. Background Information
The primary or traditional method for correcting vision defects, such as, correcting myopia, hyperopia, and astigmatism, comprises selection of and mounting of particular lenses in a spectacle-frame by the physician for a vision test, and the patient establishes his optimal faculty of vision based on the gradation of the test lines of a test image. In accordance with this traditional method, the patient can obtain optimally suited glasses for correction of significant, or approximate or gross, vision defects, but the method substantially may provide only for approximate or rough correction of vision defects.
This classical approach or method has now been replaced by objective metrological methods which are performed without active participation by the patient. Examples include automatic refractometers.
Next to the objective determination of significant vision defects, various topographical apparatus and devices for measuring eye aberrations, such as, aberroscopes or aberrometers, are utilized so as to determine patient-specific cornea topographies and, as well, substantially all wavefront aberrations. On the basis of such metrological data, the patients are treated, for example, by using an excimer laser system, to have specific topographies applied or formed on the cornea of the eye, which topographies are to ensure an optimal faculty of vision (compare: P. Mierdel, H.-E. Krinke, W. Wiegand, M. Kaemmerer, T. Seiler, “Meβplatz zur Bestimmung der monochromatischen Aberration des menschlichen Auges {Test station for the determination of the monochromatic aberration of the human eye}”, OPHTHALMOLOGE, 1997, 94; pages 441-445, SPRINGER VERLAG, 1997).
In these determinations, or measurements or metrological approaches, a double-pass through the optics system of the eye needs to be realized due to technical reasons. The main problem with this method resides therein that the uneven or odd-valent aberrations are determined in a falsified manner. A reduction of the problem with the double-pass method can be obtained, for example, by use of different numerical apertures for the entering and exiting light. Another approach comprises inducing of a fluorescence on the cornea so as to preclude these metrological errors (compare: LASER FOCUS WORLD, April 1999, pages 35-36).
In the methods available in the state of the art, an optical apparatus or system, the eye, which is a rather dynamic system, is precisely measured and corrected, but only in a momentary or snapshot-like manner. This suggests errors, particularly in the desired correction of higher-order aberrations which preclude attainment of an optimal faculty of vision. This is indicated thereby that with the measurements of eye aberrations of eyes actually having the best faculty of vision, occasionally high aberrations are shown, and till this day it is not known with certainty whether a physical correction of the eye actually increases or even worsens the faculty of vision of the eye.
It is further known that aberrations of the human eye can be compensated with the aid of adaptive optics, so as to realize high-resolution images of the cornea for medical investigations (compare: LASER FOCUS WORLD, August 1998, pages 18-22).
A microscope with an adaptive optics is described in German patent publication No. 19 733 193 A1. This publication mentions various wave modulators.
In the paper “Supernormal vision and high-resolution retinal imaging through adaptive optics,” by Liang et al., J. Opt. Soc. Am. A, Vol. 14 (1997), pages 2884-2892, apparatus and method are described with which by way of a wavefront measurement, using a deformable mirror, the feasibility of an adaptive correction of eye aberrations as well as photographic images of the retina is achieved.
U.S. Pat. No. 5,777,719, which is incorporated by reference herein, issued to inventors Williams et al. on Jul. 7, 1998 and entitled “Method and apparatus for improving vision and the resolution of retinal images,” also describes a method and a device for obtaining improved photographic pictures of the retina, with the apparatus, using a deformable mirror, being capable of obtaining corrected pictures of the retina using a CCD-camera. At the time of the Williams invention, despite significant advances in spectacle and contact lens design, ophthalmic lenses only corrected defocus and astigmatism. Spectacles and contact lenses left uncorrected additional aberrations such as spherical aberration, coma, and a host of irregular aberrations. These high order aberrations of the eye not only blur images formed on the retina, which impairs vision, but also blur images taken of the living human retina.
Subjective refractive methods of optometrists and objective autorefractors measure defocus and astigmatism only. They cannot measure the complete wave aberration of the eye, which includes all aberrations left uncorrected by conventional spectacles. The objective aberroscope disclosed by Walsh et al. in the Journal of the Optical Society of America A, Vol. 1, pp. 987-992 (1984) provides simultaneous wave aberration measurements of the entire pupil but cannot sample the pupil with a spacing finer than about 0.9 mm (See Charman in Optometry and Vision Science, Vol. 68, pp. 574-583 (1991)). Moreover, rapid, automated computation of the wave aberration has not been demonstrated with this method.
According to Williams, a Hartmann-Shack wavefront sensor can be used in to measure the wave aberrations of the human eye by sensing the wavefront emerging from the eye produced by the retinal reflection of a focused light beam on the fovea. The wavefront sensor can be used in cooperation with an adaptive optics arrangement comprising a deformable mirror, a device that has successfully compensated for atmospheric turbulence in ground-based telescopes. Williams combined these two systems to develop a method of and an apparatus for producing ophthalmic optical elements that provide improved or supernormal vision, as well as high resolution retinal images, specifically for accurately measuring higher order aberrations of the eye and for using the data thus measured to compensate for those aberrations with a customized optical element.
In the system of Williams, the wavefront in the plane of the pupil is recreated in the plane of a lenslet array of a Hartmann-Shack wavefront sensor. Each of the lenslets in the lenslet array is used to form an aerial image of the retinal point source on a CCD camera located adjacent to the lenslet array. The wave aberration of the eye, in the form of a point source produced on the retina by a laser beam, displaces each spot by an amount proportional to the local slope of the wavefront at each of the lenslets. The output from the digital CCD camera is sent to a computer which then calculates the wave aberration and provides a signal to a deformable mirror. The deformable mirror is modified until it ultimately acquires a shape that is identical to the wave aberration measured at the outset, but with half the amplitude. This deformation is the appropriate one to flatten the distorted wavefront into a plane wave, which improves image quality.
When the reconstructed wave aberration signal reaches a predetermined value based on computer calculations, the final aberration signal can be used to produce contact lenses to correct for all of the monochromatic aberrations of the human eye or for surgical procedures.
Williams' system can also be used to provide high resolution images of the retina. The system for producing such images uses a krypton flash lamp which is designed to illuminate a retinal disk to provide an image of the retina which is reflected by the deformable mirror onto a lens and through an aperture such that the reflected image of the retina is focused onto a second CCD camera. The signals generated by the camera are acquired in a manner similar to that described above in connection with the first CCD camera and are stored for later use in the computer.